The inventive concept relates to autofocus in the field of imaging. More particularly, the inventive concept relates to optical imaging systems having an autofocus capability and to methods of achieving autofocus in such imaging systems.
Autofocus allows an imaging device of optical imaging systems to focus on a selected region whose image is to be captured. In digital signal lens reflex (DSLR) cameras, phase detection pixels are used for fast autofocus. PAF stands for phase detection autofocus or phase difference autofocus. A full PAF pixel array has a structure in which every pixel includes a plurality of photoelectric conversion elements.
When a digital camera having a PAF pixel array, for example, is out of focus, a left image and a right image represented by the output from each pixel are both blurry but there is disparity between the left image and the right image. In particular, when the optical axis of a photographic lens of the camera is not coincident with the central axis of the image sensor of the camera, the blurriness value of each image varies throughout the image sensor. Thus, using the disparity from images having irregular blurriness values to automatically control the focus of the lens, i.e., to perform an autofocus, may still not bring the image into precise focus.